You'll need to be DS member for at least 15 days.
You'll need to have at least 30 post.
You will need a PayPal account, which can be created for free here.
Your PayPal account must be based in the United States or Canada.
Your PayPal account must be a verified account, which means you have confirmed your identity to PayPal using a Credit Card or Bank Account. For more information, see PayPal's Verification F.A.Q. page.

So, how do they know about your paypal account when there's no place to enter it. I have a verified paypal account, but don't know what to do next. Is it automatic after you hit 30?

it has to be the same email address you used to register here. That's how they do it. Once you have over 30 posts, you can click on any seller's badge under their username and it will take you to the application page